When you run a "ps" ( = process status) on the Tomato-prompt (either through ssh or telnet), you'll see that syslog is running with the "-m 60" parameter. Hence the "MARK" every 60 minutes.
If it is really that annoying to you, you could kill the syslog-process and (re)start it from the prompt without that specific parameter. Frankly I don't care it does...

The "unknown" is supposed to be the WRT54's hostname. Maybe you should give your Linksys a name in Basic --> Identification --> Hostname, so it shows up? I use plain "linksys" for the hostname.